This application claims priority of Japanese patent application number 2000-082992, filed Mar. 23, 2000.
1. Field of the Invention
This invention relates to a wafer polishing apparatus. More particularly, this invention relates to a polishing apparatus for polishing semiconductor wafers using chemical mechanical polishing (CMP).
2. Description of the Related Art
Miniaturization of ICs (integrated circuits) has made progress in recent years, and IC patterns are being formed in multiple layers. A surface of a layer on which such a pattern is formed unavoidably has an unevenness to a certain extent. The prior art technology forms, as such, a pattern on a previous layer. However, the greater the number of layers and the smaller the widths of lines and the diameters of holes, the more difficult it becomes to form satisfactory patterns and the more likely it becomes for defects to occur. Therefore, it is a customary practice to planarize the surface of a layer having a pattern formed thereon and then to form the pattern of a next layer. A wafer polishing apparatus (CMP apparatus) using a CMP method has been employed for polishing a wafer during the formation process of an IC pattern.
The wafer polishing apparatus includes a disc-like polishing table (platen) having a polishing cloth (polishing pad) bonded to one of the surfaces thereof, a plurality of polishing heads each holding one of the surfaces of a wafer to be polished and bringing the other surface of the wafer into contact with the polishing cloth, and a head driving mechanism for relatively rotating these polishing heads on the polishing table. The wafer is polished as a slurry containing abrasive particles is supplied between the polishing cloth and the wafer.
The polishing cloth is generally made of a polyurethane, or the like, having flexibility. As the polishing operation proceeds, wear or clogging occurs in the surface of the polishing cloth, and problems such as degradation and smoothening of the polishing cloth, and a drop in its polishing efficiency, occur.
Therefore, the wafer polishing apparatus according to the prior art is equipped with a dresser for regulating the surface of the polishing cloth so as to cope with the wear of the surface of the polishing cloth, adhesion of polishing chips or clogging by the slurry during the polishing operation. When the surface of the polishing cloth must be regulated, a grinding wheel head of the dresser is brought into contact with the polishing cloth to prevent clogging of the polishing cloth.
This regulation processing of the polishing cloth is generally referred to as xe2x80x9cconditioning processingxe2x80x9d of the polishing cloth. The conditioning processing is conducted when a new polishing cloth is fitted to replace the used polishing cloth with degradation of the polishing cloth. This is because, the surface of the new polishing cloth is not sufficiently compatible with the slurry, and the polishing condition is different between the new polishing cloth and the polishing cloth used to certain a extent, causing a difference in the wafer condition after polishing. To avoid this problem, an initialization processing is carried out to regulate the surface of the new polishing cloth by polishing a dummy wafer for a certain period of time when the new polishing cloth is used afresh.
The grinding wheel head of the conventional dresser is fixedly mounted to a main body of the dresser, and cannot therefore conduct regulation in conformity with the surface condition of the polishing cloth. Therefore, if the polishing cloth has any undulation, dressing cannot be conducted under the constant condition, a polishing ratio does not become constant, and the processing condition of the surface of the wafer does not become uniform.
In view of the problems described above, it is therefore an object of the present invention to provide a wafer polishing apparatus equipped with a dresser capable of conducting a dressing operation under a constant condition in conformity with a surface of a polishing cloth.
A wafer polishing apparatus according to one aspect of the present invention includes pushing means for idly supporting a grinding wheel head in such a manner as to be capable of moving inside a dresser main body, and capable of regulating a pushing force of the grinding wheel head to a polishing cloth. Therefore, regulation can be made in conformity with the surface of the polishing cloth under a constant dressing condition and eventually, the surface of a wafer can be polished uniformly.
A wafer polishing apparatus according to another aspect of the present invention stipulates that the pushing means is an air bag, and its function and effect is substantially the same as that of the wafer polishing apparatus described above.
A wafer polishing apparatus according to still another aspect of the invention includes a washing tank for grinding wheel heads, disposed adjacent to a platen. Since the grinding wheel heads are immersed in washing water inside the washing tank during polishing of the wafer, that is, during a non-conditioning work, drying of slurry adhering to the grinding wheel heads can be prevented and the slurry can be washed away. In this way, the conditioning work can be carried out satisfactorily.
A wafer polishing apparatus according to still another aspect of the invention includes a brush that is detachably fitted to a bottom part of the washing tank. Consequently, washing of the grinding wheel heads can be conducted more satisfactorily, and the brush can be exchanged easily.
The present invention may be more fully understood from the description of the preferred embodiment of the invention set forth below together with the accompanying drawings.